The present invention relates to an engine misfiring determining device for determining a misfiring state of each cylinder based on variation of engine momentum of the cylinder.
In general, the ideal combustion of a multi-cylinder engine keeps the same process at each cycle for the purpose of obtaining a stable output. The multi-cylinder engine, however, may be subject to vary in combustion because;
(1) An intake gas distribution factor is disproportioned by some factors such as a complicated form of an intake pipe and intake air interference between both cylinders,
(2) The cylinders have respective combustion temperatures which are slightly different among them and are caused by respective coolant routes,
(3) The cylinders are subject to variation in dimensions of some factors such as respective combustion chamber volumes and piston shapes, and
(4) The cylinders are subject to slight variation in air fuel ratio, which variation results from the difference of a fuel injection caused by the manufacturing errors of injectors.
The so-called combustion variation has been traditionally reduced to a minimum by controlling the air/fuel ratio and ignition period of each cylinder. Recently, however, the automobiles have been using a high-performance engine which keeps higher output and fuel consumption lower. When degradation or failure occurs in some components such as an injector and an ignition plug, this type of engine may intermittently cause a misfire, thereby lowering the output.
A driver may often keep a car with the multi-cylinder engine driving even if one cylinder of the engine suffers from an intermittent misfiring. Moreover, the driver cannot understand if the misfiring is transiently caused or results from the degradation of an injector or an ignition plug.
For detecting how each cylinder is combusted while driving a car, a Japanese Patent Laid-open No. 61-258955 (1986) has proposed the method comprising the steps of comparing a difference between a maximum value and a minimum value of an engine rotation speed at the previous combustion stroke with that at the current combustion stroke, determining if the compared value is within a predetermined reference value for grasping how each cylinder is combusted, if the number of combustion abnormals reaches a predetermined value, determining that a misfiring occurs, and issuing an alarm to the driver.
This prior art, however, is designed to grasp the combustion variation of each cylinder based on the difference between a minimum engine rotation speed and a maximum engine rotation speed of a combustion-stroke cylinder. In actual, the rotation speed of the engine being combusted rises abruptly and the engine is subject to relatively large load, thereby varying an acceleration more. It results in being unable to specify a maximum value of an engine rotation number and lowering the degree of accuracy about determining when a misfiring occurs.